Maté is a tea-like drink that is very popular in South America, particularly so in Argentina. Phil chose it as a name for TinyOS VMs because it is a hot, caffeinated beverage that is not coffee: it's a VM distinct from all of the Java permutations.

You traditionally drink maté from a gourd, using a long metal straw with a filter on the end, called a bombilla (hence the name of the stock VM used in the tutorials). The drink's name comes from the plant whose leaves are used: Yerba Maté.